The present invention relates to a method of forming a band for a tire, and particularly to a method of folding both edge portions of a ring-like band and assembling beads on both the edge portions of the band, and its apparatus.
As the art related to the present invention, the present inventors have examined such a method of forming a band as shown in FIG. 12.
First, a forming drum 04 expansibly divided is supported by a supporting shaft 03 projecting from a bead ring holder 05 (see FIG. 12(1)). A band 01 is fitted around the forming drum 04, and the forming drum 04 is expanded up to a specified maximum diameter (see FIG. 12(2)).
Then, on both sides of the band 01, the above bead ring holder 05 and the similar bead ring holder 06 are positioned in such a manner as to be coaxial and symmetric with respect to the band 01. Subsequently, bladders 07 and fingers 08 are respectively projected from these bead ring holders 05 and 06 (see FIG. 10(3)).
The bladders 07 are inserted within edge portions 01a of the band 01 extending from the forming drum 04. The fingers 08 expansibly divided in the circumferential direction are first disposed along the outer sides of the edge portions 01a in the expanded states, and subsequently contracted. Consequently, the edge portions 01a are disposed along the shoulder portions of the forming drum 04 and are further reduced in diameter.
Next, the bead ring holders 05 and 06 advance at such positions as to surround the edge portions 01a thus reduced in diameter, and beads 02 held by the bead ring holders 05 and 06 are mounted around the edge portions 01a (see FIG. 10(4)).
The bead ring holders 05 and 06 are separated from the band 01 (see FIG. 12(5)), and thereafter the bladders 07 are swelled while the bead ring holders 05 and 06 are again brought close to the band 01 (see FIG. 12(6)). The edge portions 01a are folded on the bead 02 by the swelled bladders 07, and thus the band 01 is formed such that the beads 02 are wrapped by the edge portions 01a folded as shown in FIG. 12(7).
The above-described band forming method, however, has the following disadvantage:
When a plurality of fingers 08 circumferentially divided are engaged with the edge portions 01a of the band, the center axis of the fingers 08 is sometimes deviated from that of the forming drum. In the event the plurality of fingers 08 are off-center, certain fingers are contacted with the edge portions 01a earlier in time, and other fingers are contacted with the edge portions 01a later in time. Accordingly, when the off-centered fingers 08 are contracted, as shown in FIG. 13, the earlier contacted fingers 08a squeeze the edge portions 01a deeply, and the later contacted fingers 08b squeeze the edge portions 01a less deeply. As a result, there occurs a variation of squeeze amount in the circumferential direction of the band.
Further, since the fingers 08a earlier contacted with the edge portions 01a receive a large reaction force from the band, they are susceptible to deformation, and to significant fatigue. In addition, the area of the edge portions 01a disproportionately squeezed by the fingers 08a tends to generate wrinkling.
In the process shown in FIG. 12(4) in which the beads are mounted around the edge portions 01a, the beads 02 released from the bead ring holders 05 and 06 are not supported from the inner peripheral surface side. Accordingly, the beads 02 tend to be easily moved and are difficult to be stably located at specified positions. Consequently, there is generated a variation in the length of a ply between the right and left beads 02 and 02.
The above-described disadvantages cause variations in the qualities of the bands, which deteriorates the uniformity of a tire.